Enter last name first (Hitchcock, Alfred). You may find two listings for a director one with name and one with name and dates. Try both listings.
Omit initial articles (Mariachi, Crying Game).
Natural language searches for words and "exact phrases" in title, subject and content notes. The order in which you enter words into the search box is important. If you are successful in finding a title with keyword, look at the item's subject heading, which can focus your search to like items.
For more information on Keyword
Using LC Subject headings (e.g., War Films, Parent and Child, or Feature Films "country"). There is a 5 vol LCSH thesaurus for subject terms. Ask at the SSHL reference desk.